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[on:]

Hey all,

I was doing some looking around and didn't see if this would be kosher or not.

I have a power hungry sensor, and an Xbee connected to an arduino, and I need a nice big battery to power it for a long time. Not sure why, but the 9 volts i'm connecting to it aren't doing the job. I get around 20 minutes or sometimes less out of them before the Xbee starts failing. I was thinking of hooking up one of those big 6 volt battery's to give me a nice long time. Would this work? Should I connect it to the power connector (same as 9 volt) with a regular plug, or should I do something else? Any other inexpensiveish battery solutions for getting a long time with batteries (put 9volts in parallel, ? etc...)?

Thanks all!

[Reply #1 on:]

4 AA or bigger cells in series should be OK but marginally so as the regulator wants to see about a volt more in than it's output voltage for proper operation, there is a diode in series with the DCin jack + connection and that leaves 6V4 - .7 (4 X 1V6 = 6V4) or 5V7 to the regulator which should work ok for all but the highest current loads > 300 400 mA. The Problem is that the batteries output voltage will fall during discharge. A new unused AA Alkaline cell will measure about 1V65 - 1V7 and is considered dead at .9 - 1V1. 4 X 1V1 = 4V4 and the minimum required voltage is 5V7-8. 3AA batteries connected to the 5V source on the Arduino or 5 AA batteries connected to DCin should work fine. If the AA batteries aren't big enough (enough current/time or AH capacity) you can always go to a "C" or "D" sized cell, the voltage will remain the same but the larger batteries have higher AH capacity and thus are better candidates for powering your project.

Bob

[Reply #2 on:]

Thanks for your answer Bob! It has alot of information i'm having trouble deciphering, but I think I get the gist. So You are saying 4 'D' or 4 'C' Cells will also not harm the arduino? And also, do you think that the big 6volt ought to be ok? http://salestores.com/stores/images/images_747/MN908.jpg (For reference)

What is "4V4", "1V7" etc...? I have never seen "XVX" before and am not sure what you mean

Thanks again for the help!

[Reply #3 on:]

What is "4V4", "1V7" etc...? I have never seen "XVX" before and am not sure what you mean

Yes you have, it's on the Arduino board. Look at the power header next to the analog in pins... It's short hand for "4.4V". 

If you're killing 9V batteries in 20 minutes the isn't a surpise.  They aren't designed for more than 30mA. Above that and their life drops expontiontially.  Even 6 AA cells will work significantly better than a small 9V.

6V through the on board regulator is iffy at best. Draw too much current and it simply won't work.

[Reply #4 on:]

No I said 3 cells (4V5) connected to the 5Volt  source or 5 cells (7V5) connected to the DCin jack. I also said that for light loads 4 cells might work although you may have 2 problems. The first and obvious is that a batteries voltage decreases with use so at some point the battery is going to approach the point where it is below the required input voltage and that that point might well be above the "dead" cell voltage (.9V to 1V1) and second that even good new cells would be an issue with a heavy load as their terminal voltage will fall far enough to make the power supply unstable. which brings us back to 3 cells on the 5V source or 5 cells on the DCin jack.

Bob

[Reply #5 on:]

I drive atmega328 chips directly with 4 AA NiMh cells, which have a slightly lower voltage.

[Reply #6 on:]

Well yes of course at 1.25 - 1.3V terminal voltage 4 X 1.25 = 5V great for the 5V source but a poor idea on the DCin jack as the regulator will only have 4V3 on it's input terminal. The recommendation I usually make is 3 cells (Alkaline) on the 5V source and 5 cells on the DCin jack. It has always worked for me. However be most careful of the DCin connection on the shield connector as there is no protection there as there is on the DCin jack.

Bob

[Reply #7 on:]

Thanks for clearing up the 4v5 thing! Now i'll know it!

As for the other info, it all sounds good! I'll look up the data spec sheet on the regulator to see the most voltage I can put through it!

Thanks and i'll make sure not to use the 6v battery, since it sounded like you did not think it would be a good idea. I'll see maybe i'll put two of those in (in series), so it bumps it to 12v which the regulator will not struggle with, unless it pumps too many amps in for the regulator. I'd rather major overkill (safely) and get like 5 hours of strong battery life than have to take apart my rig and change batteries every 20 mins.


Thanks all!

[Reply #8 on:]

If you value your Arduino and all and sundry connected to it BY ANY MEANS POSSIBLE IF you intend to load it to the Max... Keep the PSU output (Mains Operated) to 7V5. There are any number of "Switcher" type Mains PSU's that are and can be had for cheap... The easiest way to tell them apart is the Switcher types are about 1/3 the weight of a transformer type and the Switchers are "Usually" (I've not found one that wasn't) spot on as to the marked voltage being accurate form 0 to full load current.
If you are going to use batteries into the DCin jack by all means keep that voltage to the equivalent of 5 Alkaline cells in series. All of this is to avoid overheating that regulator...  data sheet says 165C... Keep it below 90C for a long and happy life.

Bob

[Reply #9 on:]

4 AA or bigger cells in series should be OK but marginally so as the regulator wants to see about a volt more in than it's output voltage for proper operation,

Batteries don't provide 1.5V for most of their life. They provide it for the first 5% or so then rapidly drop down to 1.3.

[Reply #10 on:]

Which is the exact reason that I suggested 5 Alkaline (5X 1.3 = 6.5V) And why I suggested that 5 NI-MH or NI-CD batteries would work because the NI-MH or NI-CD batteries have a reasonably "flat" discharge curve @ ~ 1.2V for about 80% of their effective charge life. I "Did" batteries for 15 or 20 years as design subjects and as actual parts, 95% of my work from 1998 to 2004 or 5 was on solar powered "Process" controllers for the irrigation industry. They were radio controlled valve controllers that operated a bi-stable or latching solenoid and charged accurately an SLA battery by voltage and tailored to temperature as the optimal charge value is different as the temperature changes being worst at low temps...

Bob